Making a Murderer is Making Viewers Curious About Brain Fingerprinting

After making its premiere in December 2015, the 10-part Netflix docuseries Making a Murderer helped usher in a new genre in streaming entertainment: true crime binge-watching. Viewers were gripped by the story of Steven Avery, a junkyard owner accused of murdering freelance photographer Teresa Halbach in 2005, and the dubious testimony of Avery's 16-year-old nephew—and alleged co-conspirator—Brendan Dassey. Avery had been convicted of a separate crime once before and served 18 years in prison before DNA exonerated him. Holes in the state of Wisconsin’s argument in the Halbach case abound, and grassroots efforts sprung up to argue that Avery had once again been wrongly convicted.

In episode two of season two, which launched on Netflix last week, Avery’s new defense attorney, Kathleen Zellner, asks Avery to submit to a curious examination informally known as “brain fingerprinting.” Wearing a head-mounted sensor that looks a little like the Cerebro helmet donned by Professor X in the X-Men comics and films, Avery is exposed to details of the crime only the perpetrator would know. The sensor can purportedly pick up the electrical signals in the brain of someone experiencing a wave of recognition, indicating they might be the guilty party.

In an otherwise grounded show, this felt like an excerpt from a science-fiction series. Is brain fingerprinting really reliable?

The forensics community isn’t really sure.

The test, which was developed by Lawrence Farwell, Ph.D. and first used in an active criminal investigation in 1999, looks for the P300 response—a surge of electrical activity in the brain roughly 300 milliseconds after a person sees something familiar to them, usually a written detail or image. Instead of looking for a physiological response in a polygraph, or “lie detector” test, Farwell’s method confines its reading to the brain via an EEG wave.

Farwell states that the test, which he calls Farwell Brain Fingerprinting, has never resulted in a false-positive or false-negative result. He says research supervised by the FBI, the U.S. Navy, and the CIA has confirmed its accuracy, and Farwell has published papers about the technique in scientific journals. In a case described on Farwell’s website, convicted murderer Terry Harrington was exonerated after he passed a brain fingerprint test and an eyewitness subsequently recanted her incriminating testimony. Farwell even offers a $100,000 bounty to anyone who can beat the test, a prize he says has yet to be claimed.

Critics of Farwell’s technique say his peer-reviewed studies have been limited to just 30 participants total, a small sample size. One study comparing the P300 response to the polygraph found some guilty subjects passed the brain fingerprint test simply by not paying attention to the images meant to trigger a response. Additionally, there have been relatively few tests conducted on truly guilty parties with psychopathic or mentally ill pathologies.

In short: There just isn't enough data to show that brain fingerprinting is as accurate as Farwell claims—or that it should be admissable in court. As for Avery: He passed his test with flying colors.